In a blood test, the number (concentration) of red or white blood cells in the blood may be measured together with the concentration of other components such as glucose, albumin and calcium. The concentration measurement of such components is performed by an optical method. Specifically, the measurement is performed by applying a sample onto a reagent pad of a test piece having been impregnated with an appropriate reagent, and then determining the degree of the color development based on the reflection of light from the reagent pad. The number of blood cells varies between individuals. Thus, in measuring the concentration of a component other than the blood cells, it is necessary to avoid the measurement error due to the blood cell components. Accordingly, in such measurement, the whole blood is subjected to centrifugal separation to cause the blood cell components to precipitate, and then the supernatant fluid is applied to the reagent pad as the sample.
To automatically perform such measurement, an analytical apparatus incorporating a centrifugal separator has been proposed (e.g. Patent Document 1). The centrifugal separator of the analytical apparatus disclosed in this document performs centrifugal separation with a container mounted to a rotor. In this analytical apparatus, when the container is rotated, air flow is generated in the container, so that the liquid retained in the container evaporates. When the liquid retained in the container evaporates, the amount of liquid (the concentration of the detection target component in the liquid) changes to result in a measurement error. To prevent the liquid from evaporating, a container provided with a lid is often used.
However, the provision of a lid for a container increases the number of parts and the material cost. Further, the step of mounting a lid to a container deteriorates the efficiency of the manufacturing process. Since the lid of the container is provided for preventing the liquid in the container from evaporating, it is desirable to make the opening diameter of the lid as small as possible within the range in which a nozzle of a pipette unit can be inserted. Therefore, to take the liquid after centrifugal separation by using a pipette unit, it is necessary to accurately position the opening of the lid. As a result, the structure of the apparatus becomes complicated, so that the manufacturing cost increases.
Patent Document 1: PCT WO02/016043